<?php

$grades = array("一","二","三","四","五","六","七","八","九","十","十一","十二");
?>

<form>
    <select name="grade">
        <?php foreach($grades as $value) :?>
        <option value="<?php echo $value;?>">第 <?php echo $value;?>周</option>
        <?php endforeach; ?>
        
    </select>
</form>

